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Electronic structure and spectroscopy of radicals in the gas and condensed phases

ELECTRONIC STRUCTURE AND SPECTROSCOPY OF RADICALS IN THE GAS
AND CONDENSED PHASES
by
Piotr Adam Pieniazek
A Dissertation Presented to the
FACULTY OF THE GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
DOCTOR OF PHILOSOPHY
(CHEMISTRY)
August 2008
Copyright 2008 Piotr Adam Pieniazek

Understanding radicals is central to understanding the mechanics of chemical change. In this work, quantitative and qualitative methods for the description of the electronic spectroscopy of open-shell species in the gas and condensed phases are developed.; Dimer radical cations are important model systems for studying ionization and charge transfer processes. Achieving a reliable theoretical description for these systems is difficult due to the symmetry-breaking of the open-shell Hartree-Fock reference and near-degeneracies. The equation-of-motion coupled-cluster for ionization potentials (EOM-IP-CC) method implemented and benchmarked here remedies these problems by using the corresponding closed-shell reference. It is combined with a qualitative Dimer Molecular Orbitals -- Linear Combination of Fragment Molecular Orbitals (DMOLCFMO) framework to elucidate the electronic states of benzene dimer and water dimer cations. In the former case the geometry of the ground state changes from a T-shaped neutral to a displaced sandwich cation. Charge resonance bands, whose spectral location and intensity are sensitive to the geometry of the system, are present in both isomers. A reordering of electronic states in the local excitation region in the sandwich structure is observed. For the water dimer vertical ionization occurs from the hydrogen-bond donor and induces a proton transfer reaction. The evolution of the electronic spectroscopy along the reaction coordinate is studied. The initial spectrum consists of mixed local and charge-transfer excitations, while the spectrum of the final product resembles that of the hydroxyl radical product. An empirical correction to the density functional theory (DFT) approach used in larger condensed phase Car-Parrinello simulations is benchmarked.; A fully condensed phase treatment is applied for the cyano radical in water. Conflicting assignments appeared in the literature as to the position of the absorption band of aqueous CN. Classical molecular dynamics simulations are combined with accurate ab initio calculations to unravel the effect of water on the two lowest electronic states of cyano radical. Accurate dimer calculations are used to parametrize the force field. A minor blue-shift of the intervalence transition energies is observed, contradicting previous experimental assignments.

ELECTRONIC STRUCTURE AND SPECTROSCOPY OF RADICALS IN THE GAS
AND CONDENSED PHASES
by
Piotr Adam Pieniazek
A Dissertation Presented to the
FACULTY OF THE GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
DOCTOR OF PHILOSOPHY
(CHEMISTRY)
August 2008
Copyright 2008 Piotr Adam Pieniazek